Part 1: learn what we can about this extinction. Who? What? Where? and possible causes. What is anoxia and was it involved? If so, how?
Does animals and plants going extinct somehow fit into global carbon cycling and CO2 in the atmosphere? And where would H2S fit into that?

Anoxia: A total decrease in the oxygen levels; an extreme decrease in oxygen availability.

Any suggestions on organization for the PowerPoint?


Perhaps start out with an overview of the 5 major mass extinctions in history you listed, and talk about impact causes versus biotic and ecological causes for extinction. Then say we will talk about the PT and the Ordovician.

definitely start with the PT extinction, because he said that should comprise 60 to 70 percent of the presentation.

Talk about how PT is the biggest extinction, the percents of extinction, and the variety and names of some organisms killed. talk about Panthalassa Sea.

Theories for extinction (in multiple slides):
Volcanism à CO2 emissions à global warming. Then introduce anoxia, and how global warming affects that in the oceans: high temperatures + deep sea Anoxia à H2S (poisonous) à depleted ozone à UV radiation. (Cool term: ever-worsening positive-feedback loop, the "runaway-greenhouse")

Then Ordovician extinction: smaller part of presentation. Global cooling --> glaciation --> dropped sea levels, etc.

Then summarize the main differences in causes and effects of the two extinctions (also that the Permian was at least twice the magnitude of the Ordovician extinction, the second biggest).

Then talk about today's conditions... And compare, concluding on which extinction would be more likely to occur today (PT is what I've gathered I think).

- zgentes zgentes"Over the past century and a half paleontologists have used ammonoids, bivalves, and now conodonts to progressively divide the Permian and Triassic into a sequence of series, stages, and at the finest level of detail, biostratigraphic zones" (Erwin)

The end-Permian extinction marks the end of marine communities dominated by the sessile, epifaunal filter-feeding articulate braciopods, bryozoans, crinoids, and other pelmatazoan echinoderms, but this extinction also led to evolutionary opportunities and more mobile marine organisms (such as mollusks).

Information we need:
  • How/Why. What are the processes involved with these two extinctions? How are they different?
  • How is H2S (Hydrogen Sulfide) involved in one or both of these?
  • Are there any "symptoms" appearing today that also appeared at or around the time of the Ordovician and P/T extinctions? If so, what are they?
  • Explain each step involved that led to each of these mass extinctions, and show how they were different.
  • Where did the extinctions occur?
  • What biota were affected, and how.
  • What hypothesis are out there that suggest the causes for these extinctions?
  • What are all of the major/mass extinctions in Earth's history (I know there were 5 in the Paleozoic era, but there were also more in the Mesozoic and Cenozoic).
  • Of the two mass extinctions being compared here (Late Ordovician and P/T), which of the causes is most likely to occur today that would effectively result in another mass extinction?

Information I have so far:

Sheehan, Peter M., 2001, The Late Ordovician Mass Extinction, Annual Reviews: Earth Planetary Science, 29:331-64.

- Several continental plates were spread around the equator.
- Greenhouse gasses caused sun to be 5% dimmer.
- Paleozoic evolutionary fauna in the oceans (less diverse than today’s faunas).

Late Ordovician
  • Mass extinction (better understood than P/T extinction)
    • Caused by impact event.
    • 2 environmental factors:
  • Cooling global climate/glaciations; because most of the fauna was fit only for Greenhouse temperatures.
  • Decline in sea level; drained seaways.
    • “The Ordovician mass extinction took place after the Paleozoic EF radiated and established a remarkable plateau of diversity that lasted until the end-Permian Extinction.”
  • By mid-Silurian, marine family diversity rebounded
    • “The Ordovician extinction was severe in terms of the number of taxa lost but was less significant in terms of the ecologic consequences.”
  • Glaciations in high altitudes. Major glaciations occurred.
    • This cooling event was relatively rapid, which did not allow for Ordovician biotas time to adapt (in contrast to the Pleistocene glaciation, which was much more gradual).
  • Gondwana landmass approached the South Pole.
  • Atmospheric CO2 was much higher than today (by 16 times)
    • This higher level during the Ordovician can be explained by an increase in volcanic gasses being released, by ~2.2 times more than recent levels.
  • Weathering Hypothesis:
    • Mountain building during the Late Ordovician resulted in atmospheric consumption of C02 due to the weathering and exposure of silicate terrains.
    • Ice sheets formed, reducing silicate weathering, followed by an increase in pCO2 by 16 times PAL. This Greenhouse effect then ended the glaciation event.“
    • Physical evidence for glaciations is limited, but isotopic studies suggest Silurian glaciations may have occurred.”
    • “The sea level fluctuations during the Silurian could have been driven by advancing and retreating ice sheets.”

Summary: Glaciation began, sea level resided, global climate changed, and oceanic circulation increased. Then, when the period of glaciation was ending, sea level rose, climate returned to preglacial conditions, and oceanic circulation slowed. Biota in epicontinental seas was more strongly affected by the decline in sea level than biota in open marine settings. Also, tropical biota was affected less than biota living in higher latitudes.

Notes on the Ordovician Extinction:

  • Finney, Stanley C.; Berry, William B. N.; Cooper, John D.; Ripperdan, Robert L.; Sweet, Walter C.; Jacobson, Stephen R.; Soufiane, Azzedine; Achab, Aicha; Noble, Paula J., 1999, Late Ordovician mass extinction: A new perspective from stratigraphic sections in central Nevada, Geology, Geological Society of America, Vol.27, No. 3, p.215-218.

  • Considered very different than most mass extinction events.
    • Only one that can be linked to glaciation and glacioeustatic sea level drop.
  • Eliminated 60% of marine genera.
  • Second greatest of the five Phanerozoic mass extinctions.


Notes on the P/T Extinction:

  • Stromatolite abundance increased after the P/T extinction. The extinction reduced metazoan activity enough to allow this resurgence.
  • The P/T mass extinction is the largest extinction event in Earth's history.

There is evidence found in oceanic sediments from the Late Permian to Late Triassic, which yielded chemical evidence of an ocean-wide spread of the H2S bacteria. This evidence was also found in strata from the once-shallow marine settings of the P/T boundary, which suggests that a lack of oxygen also reached the surfaces.
Note: These microbes can only survive in an oxygen-free environment, however they do need sunlight for their photosynthesis.

  • "The end-Permian mass extinction coincides with one of the most massive volcanic eruptions of the past 600 million years.... Global cooling from erupted dust, followed by global warming from clouds of carbon dioxide and acid rain from billowing sulfur are commonly proposed links between volcanism and extinction, but are difficult to test." (Erwin, Douglas H., 2006, Extinction: how life on earth nearly ended 250 million years ago, Princeton University Press, Princeton, New Jersey, pp.10-15)
  • There is no solid evidence of an impact event.
  • "...The various anoxia hypotheses (there are at least three) suffer from an inability to explain the terrestrial extinciton." (Erwin, Douglas H., 2006, Extinction: how life on earth nearly ended 250 million years ago, Princeton University Press, Princeton, New Jersey, pp.10-15)
  • The P/T mass extinction is similar to the Cretaceous-Teriaty mass extinction.


H2S (Hydrogen Sulfide)

- Hydrogen sulfide is a colorless gas with an offensive stench and is said to smell like rotten eggs. (

ScienceDaily: "Hydrogen Sulfide, Not Carbon Dioxide, May Have Caused Largest Mass Extinction"

"Today [tiny photosynthetic green sulfur bacteria] are found, along with their cousins, photosynthetic purple sulfur bacteria, living in anoxic marine environments such as the depths of stagnant lakes and the Black Sea, and they are pretty noxious characters. For energy, they oxidize hydrogen sulfide (H2S) gas, a poison to most other forms of life, and convert it into sulfur. Thus, their abundance at the extinction boundaries opened the way for a new interpretation of the cause of mass extinctions" (Ward, 2006).

Major Extinctions:

- At first scientists thought that 4 out of these 5 extinctions where caused by comet or asteroid impacts, however as new data accumulated some things did not add up to support this theory. New information suggested that the P/T extinction was gradual or drawn-out, spanning over hundreds of thousands of years. In addition to this information, data showing a rise and fall of the atmospheric carbon suggested a series of long cycles (Ward, 2006).

Misc Theories:

Volcanic activity was once associated with most of the mass extinctions because they could potentially raise the CO2 levels in the atmosphere (which reduces oxygen and leads to global warming), however this effect could not account for the massive marine extinctions at the P/T boundary. Nor could they also account for the death of land plants because vegetation would thrive on increased CO2 levels (Ward, 2006).

Causes/Theories for Extinctions

P/T Extinction:
(from wikipedia)
  • Impact
    • The evidence of an impact for the C/T extinction led geologists to speculate that such events may have played a part in other mass extinctions, including the P/T extinction.
    • Evidence for impacts that occurred in the Permian includes rare grains of shocked quartz (found in Australia and Antarctica); samples of containing trapped extraterrestrial noble gases; meteorite fragments (found in Antarctica); and grains rich in iron, nickel, and silicon which may have been created by impact.
      • The shocked quartz was found to be unrelated to the P/T extinction.
      • Several possible impact craters have been proposed, however the cases that have been identified have not been proven, nor is it likely that the remaining crater still exists (a side theory to this is that impacts may cause after affects that lead to additional extinctions).
    • An impact event would explain why species did not have time to adapt to any changes.
  • Volcanism
    • A major volcanic event spread flooded basaltic lava over 2,000,000 square kilometers. This occurred at the very end of the Permian.
      • This eruption may have caused dust clouds and acid aerosols, which block out sunlight.
      • ~20% of this volcanic output was pyroclastic (explosions of ash and debris).
      • These eruptions alone are not likely enough to have caused the mass extinction.
  • Methane Hydrate Gasification
  • Sea Level Fluctuations
    • Marine regressions expose relatively shallow marine habitats, destroying part of the bottom of the food chain which in turn increases competition for food sources.
    • There is only some correlation between marine regressions and mass extinctions.
    • It is also suggested that sea-level changes may result in altered sediment depositional rates which affects water temperature and salinity. These changes may cause death of some marine life.
  • Anoxia
    • Evidence found in uranium/thorium ratios shows that oceans became severely anoxic by the end of the Permian.
    • The possible sequence of events leading to anoxic oceans may have involved a period of global warming that reduced the temperature gradient between the equator and the poles which slowed or possibly stopped thermohaline circulations. This reduction may have reduced the mixing of oxygen in the ocean (this is unlikely though).
      • There was a noticeable and rapid onset of anoxia in marine sediments around East Greenland near the end of the Permian.
  • Hydrogen Sulfide Emissions
    • The severe anoxia at the end of the Permian may have made sulfate-reducing bacteria the dominant force in oceanic ecosystems, which led to vast emissions of poisonous hydrogen sulfide that kills both plant and animal life on both land and in the sea. This may also weaken the ozone layer enough to allow fatal amounts of UV radiation to reach Earth's surface.
      • This anaerobic photosynthesis persisted into the early Triassic, which is consistent with fossil evidence for the fact that recovery from the P/T extinction was very slow.
      • This theory could explain the mass extinction of plants, which otherwise should have thrived in an atmosphere containing high levels of CO2.
      • Fossil spores from the end-Permian show deformities that could have been caused by UV radiation.
  • Pangaea
    • The formation of the supercontinent Pangaea greatly decreased the extent of shallow marine environment. It also altered oceanic circulations and atmospheric weather patterns, creating seasonal monsoons along the coasts and arid climates within the continent's interior.
    • Marine life suffered very high (but not catastrophic) rates of extinction after the formation of Pangaea (more so for marine life and less so for land life). Thus the formation of Pangaea may have had an affect on the amount of extinctions without being directly responsible.
  • Misc Combinations
    • Each possible cause led to another, creating a chained sequence, almost like a domino effect, with each event being more extreme than the previous. This results in a comination of catastrophic events that ultimately caused the mass extinction.

Ordovician Extinction:

Magnitude of PT extinction:

((I have some good comparative figures, but I can't get them on here so I will give them to you in the library tomorrow. ))

Impact from the Deep

Strangling heat and gases emanating from the earth and sea, not asteroids, most likely caused several ancient mass extinctions. Could the same killer-greenhouse conditions build once again?
By Peter D. Ward

The Meishan section across the Permian-Triassic boundary in South China is the
most thoroughly investigated in the world. A statistical analysis of the occurrences
of 162 genera and 333 species conÞrms a sudden extinction event at
251.4 million years ago, coincident with a dramatic depletion of d13Ccarbonate

and an increase in microspherules.

Pelagic cherts of Japan and British Columbia, Canada, recorded a long-term and worldwide
deep-sea anoxic (oxygen-depleted) event across the Permo-Triassic (or Paleozoic
and Mesozoic) boundary (25 2 million years ago). The symmetry in lithostratigraphy
and redox condition of the boundary sections suggest that the superocean Panthalassa
became totally stratified for nearly 20 million years across the boundary. The timing of
onset, climax, and termination of the oceanic stratification correspond to global biotic
events including the end-Guadalupian decline, the end-Permian extinction, and mid-

Triassic recovery.

Abstractexternal image 2002.gif Near the end of the Late Ordovician, in the first of five mass extinctions in the Phanerozoic, about 85% of marine species died. The cause was a brief glacial interval that produced two pulses of extinction. The first pulse was at the beginning of the glaciation, when sea-level decline drained epicontinental seaways, produced a harsh climate in low and mid-latitudes, and initiated active, deep-oceanic currents that aerated the deep oceans and brought nutrients and possibly toxic material up from oceanic depths. Following that initial pulse of extinction, surviving faunas adapted to the new ecologic setting. The glaciation ended suddenly, and as sea level rose, the climate moderated, and oceanic circulation stagnated, another pulse of extinction occurred. The second extinction marked the end of a long interval of ecologic stasis (an Ecologic-Evolutionary Unit). Recovery from the event took several million years, but the resulting fauna had ecologic patterns similar to the fauna that had become extinct. Other extinction events that eliminated similar or even smaller percentages of species had greater long-term ecologic effects.

Integrated sequence stratigraphic, biostratigraphic, and chemostratigraphic analyses of
three stratigraphic sections in central Nevada indicate that Late Ordovician glaciation-induced
sea-level fall produced diachronous, stepwise faunal turnover in graptolites, conodonts, chitinozoans,
and radiolarians, and also triggered a strong, but transient, positive __ excursion. This pattern is very different from that described for most mass extinctions.

Did a gamma-ray burst initiate the late Ordovician mass extinction?


Gamma-ray bursts (GRBs) produce a flux of radiation detectable across the observable Universe. A GRB within our own galaxy could do considerable damage to the Earth's biosphere; rate estimates suggest that a dangerously near GRB should occur on average two or more times per billion years. At least five times in the history of life, the Earth has experienced mass extinctions that eliminated a large percentage of the biota. Many possible causes have been documented, and GRBs may also have contributed. The late Ordovician mass extinction approximately 440 million years ago may be at least partly the result of a GRB. A special feature of GRBs in terms of terrestrial effects is a nearly impulsive energy input of the order of 10 s. Due to expected severe depletion of the ozone layer, intense solar ultraviolet radiation would result from a nearby GRB, and some of the patterns of extinction and survivorship at this time may be attributable to elevated levels of UV radiation reaching the Earth. In addition, a GRB could trigger the global cooling which occurs at the end of the Ordovician period that follows an interval of relatively warm climate. Intense rapid cooling and glaciation at that time, previously identified as the probable cause of this mass extinction, may have resulted from a GRB.

Aftermath of the Permian-Triassic mass extinction event: Paleoecology of Lower Triassic carbonates in the western USA :
Paleoecologic study of invertebrate faunas from three successive Early Triassic seaways reveals that biotic recovery from the end-Permian mass extinction event was slow, and that full recovery did not occur until after the Early Triassic. Simple, cosmopolitan, opportunistic generalists, and low-diversity, low-complexity paleocommunities were characteristic of the entire Early Triassic in the Western USA. An increase in guild and taxonomic diversity was observed with the addition of several new higher taxa in the late Early Triassic (Spathian) to the almost exclusively molluscan faunas of the earlier Early Triassic (Nammalian). Potential ''disaster forms'' (the inarticulate brachiopod,Lingula , and the paper pecten, Claraia) dominated the earliest Early Triassic faunas (Griesbachian) and even occurred in the late Early Triassic (normal marine stromatolites). Comparison with data on faunas from the Permian and Triassic suggests that even the most diverse Early Triassic faunas (in the Spathian) were rather low in guild diversity and species richness. These characteristics of genera and paleocommunities in the Early Triassic may be typical of mass extinction aftermaths.

Rapid eruption of Siberian flood-volcanic rocks and evidence for coincidence with the Permian–Triassic boundary and mass extinction at 251 Ma


The Siberian flood-volcanic event is the most voluminous and explosive, continental, volcanic event known in the Phanerozoic record. U–Pb perovskite and zircon ages were obtained for lavas of the lowermost unit (251.7±0.4 Ma) and near-uppermost unit (251.1±0.3 Ma), respectively, of the volcanic sequence in the Maymecha–Kotuy area, Russia. Along with stratigraphic correlations and paleomagnetic evidence, these ages suggest that rapid extrusion of the entire
not, vert, similar
not, vert, similar
6500 m thick composite sequence occurred in less than 1 million years. The time of extrusion coincides precisely with an age of 251.4±0.3 Ma previously obtained for the Permian–Triassic mass-extinction event, the most devastating biotic crisis known. Emplacement of the Noril’sk–Talnakh ore-bearing intrusions, notable for their prodigious Cu–Ni–PGE deposits, was synchronous with these two major geologic events at 251.2±0.3 Ma. The Guli volcanic-intrusive complex in the Maymecha–Kotuy area appears to represent the final mafic magmatism of the entire Siberian flood-volcanic event. Baddeleyite from a carbonatite that intrudes the complex gives an age of 250.2±0.3 Ma, and shows possible 231Pa excess. The Bolgokhtokh granodiorite stock has a zircon age of 229.0±0.4 Ma, and represents the youngest known magmatism in the region.

Comparative Earth History and Late Permian Mass Extinction
A. H. Knoll, R. K. Bambach, D. E. Canfield, J. P. Grotzinger
The repeated association during the late Neoproterozoic Era of large carbon-isotopic excursions, continental glaciation, and stratigraphically anomalous carbonate precipitation provides a framework for interpreting the reprise of these conditions on the Late Permian Earth. A paleoceanographic model that was developed to explain these stratigraphically linked phenomena suggests that the during the Late Permian introduced high concentrations of carbon dioxide into surficial environments. The predicted physiological and climatic consequences for marine and terrestrial organisms are in good accord with the observed timing and selectivity of Late Permian mass extinction.;273/5274/452

Extinction: how life on earth nearly ended 250 million years ago

By Douglas H. Erwin
(page 10 has discussion of massive volcanic eruption coinciding with extinction)


An analysis of the final stratigraphic appearances of byrozoan species and genera, compiled in a world-wide bryozoan data base, revealed three discrete Late Ordovician extinctions. A Late Carddoc (Onnian) extinction was most pronounced on the plates of Baltica and Siberia. Endemic species and genera, confined to one plate and one lithotope were most affected and the extinction was coincident with increased migrations of bryozoan genera to Baltica and Siberia. The Late Caradoc extinction may be related to decreasing provinciality and competition between migrant and stenotopic taxa. Two major extinctions occurred in the Late Ashgill. The greatest of the two is recognized at the end of the Rawtheyan. and affected primarily taxa on the North American plate. The extinction at the end of the Hirnantian affected primarily Baltic taxa. The exact timing of the end-Rawtheyan extinction in North America cannot be established owing to incompleteness of the stratigraphic record. The Rawtheyan extinction occurred during a major glaciation centered in North Africa and a regression of epeiric seas. The large majority of North American survivors of the extinction are represented by Faunas preserved on Anticosti Island. which remained submerged during the regression. This evidence supports regression as a cause of the Rawtheyan extinctions in North America. The end-Hirnantian extinctions may be related to the ensuing transgression or to a wave of faunal migrations associated with the transgression. *Bryozoa, extinctions, Ordovician, Rawtheyan, Hirnantian, North America, Baltica.

  • The Permian period was between 290 Ma and 250 Ma.
  • At that time the land was in one mass called a supercontinent. This supercontinent was PANGEA.
  • 95% of all marine life on earth was killed.
  • 70% of all land families became extinct
possible reasons for the extinction -- >